Photoelectric tube



M. c. TEVE S ET AL 2,031,864

PHOTOELECTRIC TUBE A Filed Nov. 25, 1931 ji 5 Invent ons 2!. G. Teves ad! JZJTM varaEmMen Patented Feb. 25, 1936 TABS PATENT OFFICE PHOTOELECTRIC TUBE Application November 23, 1931, Serial No. 576,836 In Germany December 6, 1930 10 Claims.

The present invention provides means for supplying the current to the photo-electric electrode of a tube, and simplifies the manufacture of the tube.

A photo-electric tube according to the invention comprises a photo-electric electrode which is separated from another electrically conducting electrode by means of a layer essentially consisting of one or more insulating or semi-conducting solid materials, said electrodes and the insulating or semi-conducting layer being provided on one another with the interposition of other layers, if desired. Furthermorethe device comprises an electron emitting body which is mounted in such a manner that the emitted electrons may'reach the photo-electric electrode. In this case the contact member of the photo-electric electrode consists as it were of an electron cloud formed in the vicinity of the photo-electric electrode. On irradiating said electrode a potential difference is set up in the device, said potential difference on closing the external circuit causing the passage of an electron current from the photo-electric electrode through the insulating or semiconducting layer to the other electrode. The electrons are supplied to the photo-electric electrode by the emitting body. The external electric circuit is connected between the photo-electric electrode and the electron emitting body.

".It is worth noticing that this body may be given either a negative or a small positive potential as well as no potential at all, with respect to the photo-electric electrode.

In many cases it is desirable to provide an auxiliary electrode between the elctron emitting body and the photo-electric electrode. This auxiliary electrode may be given such a potential relatively to the emitting body that the emitted electrons are accelerated.

If the electron emiting body emits light rays at the same time, these rays in many cases also will strike the photo-electric electrode. This exposure has a practically constant intensity, due to which a constant potential difierence will be set up in the device. In addition to this constant potential difference a light source of varying intensity may produce a varying potential difference.

If it is desired to avoid the constant exposure of the electrode by the emitting body, then a screen which is not transparent to light rays may be advantageously placed between the emitting body and the photo-electric electrode. In this case the electrons may pass round this screen,

i while the light rays are caught by it. Especially with this construction it may be desirable to use an auxiliary electrode of the type above referred to by which the electrons are accelerated.

The influencing of the potential difference set up by rays emanating from the electron emitter may also be avoided by using a body which emits electrons at a temperature at which practically no light rays are emitted. This emitter may be constituted with advantage by a cathode adapted to be heated and coated with an alkali metal. In this case the surface of this emitter and the photo-electric electrode may consist of the same a1- kali metal which is introduced in one operation into the device.

The electron emitting body may also be constituted by an alkaline earth oxide cathode (directly or indirectly heated) by which likewise almost no visible light is emitted. When forming the emitting layer by means of an alkaline earth metal precipitated from the vapour phase, the manufacture of the device may be simplified by making the photo-electric electrode of the same alkaline earth metal.

The electron emitter may also consist of a body containing a photo-electric substance so that the electrons may be liberated photo-electrically, due to which heating of the emitter is entirely superfluous.

In many cases the electron emitter may also consist of a radio-active material emitting B rays. When providing between both electrodes of the device a fluorescent material, by which is to be understood a substance which emits fluorescent rays on being struck by electrons, then the device may be used with advantage for amplifying pho- K tographs or for transforming these photographs into images of rays having other wave lengths, as described in patent application No. 571,562, filed Oct. 28, 1931.

The invention will be more clearly understood by reference to the accompanying drawing, representing by way of example, two forms of construction thereof.

Figs. 1 and 2 are difierent views of one form of construction and Figs. 3 and 4 show the other form of construction.

The photo-electric device shown in Figs. 1 and 2 comprises a bulb I made of glass, quartz or similar material to which is sealed a stem 2 having a pinch 3. This pinch carries the electrodes and the electron-emitter of the device. One of the electrodes is constituted by a zirconium plate 4 which by means of a supporting rod 5 is mounted on the pinch and is electrically connected to the supply conductor 6. The zirconium plate 4 is coated with a thin layer of zirconium oxide 1 which may be formed by superficial oxidation of the plate 4 and which is an insulating material as is well known. To the zirconium oxide layer 1 is applied a layer 8 consisting in this case of caesium and constituting one electrode of the device.

An incandescible cathode 9 is mounted on the pinch 3. This incandescible cathode, which is connected to the supply conductors Hi and II consists of a tungsten helix which is superficially coated with caesium.

On manufacturing the device illustrated first of all the oxidized zirconium plate and the tungsten helix 9 are introduced into the bulb, By heating the tungsten wire 9 in an atmosphere containing oxygen this wire is superficially oxidized, whereupon the tube is exhausted, which may be effected by means of a vacuum pump connected to the exhaust tube l2. After the exhaustion caesium is introduced into the bulb I. This caesium may be introduced into the device, for example, through the tube is. However, it is also possible to develop the caesium in the interior of the bulb l, for example by heating a mixture of a caesium compound and a suitable reducing agent. The caesium introduced into the device deposits on the zirconium oxide layer 1 and forms there the photo-electric electrode 8. At the same time part of the caesium deposits on the oxidized tungsten wire 9 thus forming thereon a high electron emitting layer. As is well known such a cathode emits electrons at very low temperatures, while practically no visible light rays are emitted. After the introduction of the caesium the tube i3 may be sealed off.

If the photo-electric electrode 8 is irradiated by means of a light source 14, then a potential difference is set up between the electrodes 4 and 8. This potential difference may cause the passage of a current through the device if an external electric circuit is connected between the supply conductor 6 and one of the supply conductors l0 and H. It is necessary to lead a current through the incandescible cathode 9 so that electrons are emitted sufficient to carry the current across the space between the electrodes. The current set up by the irradiation-may pass through the circuit without inserting therein a source of potential. Preferably, the incandescible body 9 is given a small negative potential with respect to the photo-electric electrode 8. However, a small positive voltage may also be applied to this incandescent cathode without the current direction being reversed in the circuit. Since the potential difference set up and the current resulting therefrom depend on the intensity of the irradiation, the device may be used for transforming light variations into electric voltage and current variations.

The device shown in Figs. 3 and 4 also comprises an electrically conducting electrode 4 and a photo-electric electrode 8 which are separated from one another by a layer 1. The device furthermore comprises an incandescible cathode l5 which does not emit electrons until it is heated to a temperature at which light rays are also emitted. This electrode is constituted, for example, by a tungsten wire. In order to prevent the photo-electric electrode from being influenced by the emitted light rays, a screen l6 which is not transparent to light rays is placed between .the incandescible cathode l5 and the said electrode. This screen is constituted, for example,

by a metal plate and fixed to one of the pole wires of the incandescible cathode l5. 7

Between the screen It and the electrode 8 is provided a sieve-shaped electrode l'i, having fine meshes which is fixed to a supporting wire l8 and connected to a current supply wire l9. This electrode i1 is slightly bent around the edges of the screen l6 and may serve as a grid by which the electrons emitted by the incandescible cathode l5 are accelerated and caused to move to the photo-active electrode 8. For this purpose it is necessary to apply to the electrode l! a positive tension with respect to the incandescible cathode 15 during operation.

When using the device the light source must be mounted in such manner that the quantity of rays caught by the screen 56 is as small as possible. The light source may be mounted, for example, atZll so that the rays are angularly incident.

The photo-electrode of the device may also be applied on to the wall. To this effect the wall of the tube is first of all coated, for example, with a metal layer to which is applied the intermediate layer on which the light-sensitive electrode is barium oxide which is applied to the metal plate 4 consisting, for example, of nickel. As is known, barium oxide as well as zirconium oxide is an insulating material.

If it is desired to use semi-conducting materials, then the plate 4 may consist, for example, of silver at the surface of which may be formed a silver iodide layer by the action of iodine vapour. The plate 4 may also consist of copper and be superficially oxidized thus forming a layer of copper oxide which, like the said iodide is a semi-conducting material.

It is remarked that other materials may also be provided between the electrodes 4 and 8, for example, a fluorescent material. This fluorescent material may at the same time form the insulating or semi-conducting layer 1.

In the following claims we refer to such an insulating or semi-conducting material as above described as a non-conducting material, as distinguished from such materials as are ordinarily considered conductors of electricity.

What we claim is:

1. A photo-electric device comprising an electrically conducting electrode, a non-conducting solid material thereon, a photo-electric electron emitting layer on said solid material, an electron-emitting body mounted in spaced relation with respect to said photo-electric layer, and an auxiliary electrode. interposed in the space path between the electron-emitting body and the said photo-electric layer.

2. A photo-electric device comprising an electrically conducting electrode, a non-conducting solid material thereon, a photo-electric layer on said solid material, an electron-emitting body mounted in spaced relation with respect to said photo-electric layer, and a light-opaque screen interposed in the space path between the electron-emitting body and the said photo-electric layer.

.3. A photo-electric device comprising an electrically conducting electrode, a non-conducting solid material thereon, a photo-electric layer on said solid material, an electron-emitting body mounted in spaced relation with respect to said photo-electric layer, and an auxiliary electrode and a light-opaque screen interposed in the space path between the electron-emitting body and the said photo-electric layer.

4. A photo-electric device comprising a photoelectric electrode, a solid insulating layer contiguous thereto, a second layer on the opposite side of said solid insulating layer from said photo-electric electrode, an electron-emitting body mounted in spaced relation with respect to said photo-electric electrode, and a tube surrounding said electron-emitting body and said electrode, the said device being adapted to be actuated by a light source disposed externally of said tube and directing the light from said source on said photo-electric electrode at an acute angle of incidence.

5. A photo-electric device comprising an envelope, an electrically conducting electrode in said envelope, a non-conducting solid material on said electrode, a photo-electric layer consistsaid plate consisting of an oxide of the same metal, a photo-electric layer on said layer and comprising an electron emitting metal, and an incandescible cathode in spaced relation therewith.

7. A photo-electric device comprising an electrically conducting electrode, a non-conducting solid material on said electrode, a photo-electric layer of barium disposed on said solid material, and an electron-emitting body disposed in spaced relation with said barium electrode.

8. A photo-electric device comprising an envelope, a plate of nickel in said envelope, a barium oxide layer on said plate, a photo-electric layer formed of barium and disposed on said oxide layer, and an electron-emitting body disposed in spaced relation with said barium layer.

9. A photo-electric device comprising an envelope, a plate in said envelope and formed of silver, a layer of silver iodide on said plate, a photo-electric layer on said iodide layer, and an electron-emitting body disposed in spaced relation with said photo-electric layer.

10. A photo-electric device comprising an envelope, a plate in said envelope, formed of cop- 

